Matrix metalloproteinase-2 activation in human hepatic fibrosis regulationby cell-matrix interactions

Matrix metalloproteinase-2 (MMP-2) is involved in extracellular matrix remo deling. It is secreted as a proenzyme and activated by membrane type-MMPs ( MT-MMP), such as MT1-MMP. In liver fibrosis, MMP-2 is highly expressed in m yofibroblasts and may have a profibrogenic role. The mechanisms of its acti vation in the liver are still unclear. The aim of this work was to show tha t pro-MMP-2 is efficiently activated in human fibrotic liver and to investi gate the role of cell-matrix interactions in this process, Liver specimens obtained from patients with active cirrhosis were compared to normal liver specimens. Human hepatic myofibroblasts were cultured either on plastic, fi bronectin, laminin, or on collagen I gels. MMP-2 activity was visualized by gelatin zymography. MMP-2 active form (59 kd) was detected in active cirrh osis but not in normal liver. Myofibroblasts cultured on plastic, fibronect in, or laminin predominantly expressed inactive pro-MMP-2 (66 kd), In contr ast, myofibroblasts cultured on collagen I markedly activated the enzyme. S imilar results were obtained using membrane fractions from cells previously cultured on collagen or plastic. Activation was inhibited by the tissue in hibitor of metalloproteinases-2 but not by tissue inhibitor of metalloprote inases-l, implicating a MT-MMP-mediated process. Culture on collagen I up-r egulated MT1-MMP protein detected by Western blotting, but decreased MT1-MM P mRNA, This study shows that MMP-2 is activated in fibrotic liver. It sugg ests that interactions between collagen I and myofibroblasts promote this p rocess through a posttranslational increase of MT1-MMP expression in these cells.